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Protoavis
| image = Image:Protavis 2.gif | caption = Protoavis restoration. | kingdom = Animalia | phylum = Chordata | class = Aves (disputed) | order = Saurischia or Protoaviformes Chatterjee, 1991 | suborder = Theropoda? | unranked_suborder = Tetanurae? | unranked_infraorder = Coelurosauria? | unranked_superfamily = Avialae? | family = Protoavidae Chatterjee, 1991 | genus = Protoavis Chatterjee, 1991 | species = *''P. texensis'' Chatterjee, 1991 (type) }} Protoavis (meaning "first bird") is a problematic taxon of archosaurian whose fossils have been recovered from Late Triassic deposits near Post, Texas. Much controversy remains over the animal, with many different interpretations of what Protoavis actually is existing. When it was first described, the fossils were ascribed to a primitive bird which, if the identification is valid, would push back avian origins some 60-75 million years.Chatterjee, S. (1995): The Triassic bird Protoavis. Archaeopteryx 13: 15-31.Chatterjee, S. (1998): The avian status of Protoavis. Archaeopteryx 16: 99-122.Chatterjee, S. (1999): Protoavis and the early evolution of birds. Palaeontographica A 254: 1-100. History of discovery Archosaurs discoveries are comparatively abundant in Texas, and have been recovered in some quantity since E. D. Cope worked the redbeds of the panhandle over a century ago.Cope, E. D. (1892). A contribution to the vertebrate paleontology of Texas. Proceedings of the American Philosophical Society 30:123–131. The holotype specimen of Protoavis (TTU P 9200), the paratype (TTU P 9201), and all referred materials, were discovered in the Dockum Group, from the panhandle of Texas. The Dockum dates from the Carnian through the early Norian, in the terminal Triassic and is composed of four units of decreasing age: the Santa Rose Formation, the Tecovas Formation, the Trujillo Formation, and the Cooper Canyon Formation, and the Bull Canyon Formation.Lehman, T. (1994). The saga of the Dockum Group and the case of the Texas/New Mexico boundary fault. Summarized in The Rise of Birds: 225 Million Years of Evolution, Chatterjee (1997). Specifically, Protoavis remains have been recovered from the Post Quarry Bull Canyon and Tecovas Formations, and consists of a partial skull and postcranial remains belonging to possibly several large individuals. The type material was collected from mudstone deposits in June of 1973 and initially identified as a juvenile Coelophysis bauri. The level of the Dockum group from which the Protoavis material was recovered, was most likely deposited in a deltaic river system. The bone bed excavated by Sankar Chatterjee and his students of Texas Tech University, in which Protoavis was discovered, likely reflects an incident of mass mortality following a flash flood.Lehman, T., Chatterjee, S. & Schnable, J. (1992). The Cooper Canyon Formation (Late Triassic) of western Texas. Texas Journal of Science 44: 349-355. Chatterjee, who first described Protavis, has assigned the binomial Protoavis texensis ("first bird from Texas") to the small cache of bones, allegedly conspecific. He interpreted the type specimen to have come from a single animal, specifically a 35 cm tall bird that lived in what is now Texas, USA, between 225 and 210 million years ago. Chatterjee, and a few other paleornithologists (notably Evgeny Kurochkin and Stefan Peters) have claimed that this material documents a Triassic origin of birds and the presence of a bird more advanced than Archaeopteryx. Though it existed approximately 75 million years before the oldest known bird, its skeletal structure is allegedly more bird-like.Chatterjee, S. (1991). "Cranial anatomy and relationships of a new Triassic bird from Texas." Philosophical Transactions of the Royal Society B: Biological Sciences, 332: 277-342. HTML abstract Protoavis has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at the front of the skull, suggesting a nocturnal or crepuscular lifestyle.Chatterjee, S. (1987). "Skull of Protoavis and Early Evolution of Birds." Journal of Vertebrate Paleontology, 7'(3)(Suppl.): 14A. The fossil bones are too badly preserved to allow an estimate of flying ability; although reconstructions usually show feathers, judging from thorough study of the fossil material there is no indication that these were present.Paul, G.S. (2002). ''Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins University Press, Baltimore. ISBN 0-8018-6763-0Witmer, L. (2002). "The debate on avian ancestry: phylogeny, function, and fossils." Pp. 3-30 in: Chiappe, L.M. and Witmer, L.M. (eds), Mesozoic birds: Above the heads of dinosaurs. University of California Press, Berkeley, Calif., USA. ISBN 0-520-20094-2 However, this description of Protoavis assumes that Protoavis has been correctly interpreted as a bird. Almost all paleontologists doubt that Protoavis is a bird, or that all remains assigned to it even come from a single species, because of the circumstances of its discovery and unconvincing avian synapomorphies in its fragmentary material.Nesbitt, Sterling J.; Irmis, Randall B. & Parker, William G. (2007): A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology '''5(2): 209-243.Ostrom, J. (1987): Protoavis, a Triassic bird? Archaeopteryx 5': 113-114.Ostrom, J.H. (1991): The bird in the bush. ''Nature '''353(6341): 212.Ostrom, J.H. (1996): The questionable validity of Protoavis. Archaeopteryx 14: 39-42. When they were found at a Dockum Group quarry in the Texas panhandle in 1984, in a sedimentary strata of a Triassic river delta, the fossils were a jumbled cache of disarticulated bones that may reflect an incident of mass mortality following a flash flood. Dispute Chatterjee was convinced that some of these crushed bones belonged to two individuals - one old, one young - of the same species. However, only a few parts were found, primarily a skull and some limb bones which moreover do not well agree in their proportions respective to each other, and this has led many to believe that the Protoavis fossil is chimeric, made up of more than one organism: the pieces of skull appear like those of a coelurosaur, while most parts of the limb skeleton suggest affinities to ceratosaurs and at least some vertebrae are most similar to those of Megalancosaurus, an avicephalan diapsid:Renesto, S. (2000). "Bird-like head on a chameleon body: new specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of northern Italy." Rivista Italiana di Paleontologia e Stratigrafia 106: 157–180. PDF fulltext "Everywhere one turns; the very fossils ascribed thereto challenge the validity of Protoavis. The most parsimonious conclusion to be inferred from these data is that Chatterjee's contentious find is nothing more than a chimera, a morass of long-dead archosaurs."EvoWiki (2004). Chatterjee's Chimera: A Cold Look at the Protoavis Controversy. Version of 2007-JAN-22. Retrieved 2009-FEB-04. If it really is a single animal and not a chimera, Protoavis would raise interesting questions about when birds began to diverge from the dinosaurs, but until better evidence is produced, the animal's status currently remains uncertain. Furthermore, paleobiogeography suggests that true birds did not colonize the Americas until the Cretaceous; the most primitive lineages of unequivocal birds found to date are all Eurasian. Certainly, the fossils are most parsimoniously attributed to primitive dinosaurian and other reptiles as outlined above. However, coelurosaurs and ceratosaurs are in any case not too distantly related to the ancestors of birds and in some aspects of the skeleton not unlike them, explaining how their fossils could be mistaken as avian. Paleontologist Zhonghe Zhou stated: "[Protoavis] has neither been widely accepted nor seriously considered as a Triassic bird ... Witmer, who has examined the material and is one of the few workers to have seriously considered Chatterjee’s proposal, argued that the avian status of P. texensis is probably not as clear as generally portrayed by Chatterjee, and further recommended minimization of the role that Protoavis plays in the discussion of avian ancestry."Zhou, Z. (2004). "The origin and early evolution of birds: discoveries, disputes, and perspectives from fossil evidence." Naturwissenschaften 91(10): 455-471. (HTML abstract) In discussions of evolution Scientists such as Alan Feduccia have cited Protoavis in an attempt to refute the hypothesis that birds evolved from dinosaurs.Feduccia, A. (1999). The Origin and Evolution of Birds (2nd ed.). Yale University Press, New Haven. ISBN 0-300-07861-7 However, the only consequence would be to push back the point of divergence further back in time. At the time when such claims were originally made, the affiliation of birds and maniraptoran theropods which today is well-supported and generally accepted by most ornithologists was much more contentious; most Mesozoic birds have only been discovered since then. Chatterjee himself has since used Protoavis to support a close relationship between dinosaurs and birds.Chatterjee, S. (1997). The Rise of Birds: 225 Million Years of Evolution. Johns Hopkins University Press, Baltimore. ISBN 0-8018-5615-9 "As there remains no compelling data to support the avian status of Protoavis or taxonomic validity thereof, it seems mystifying that the matter should be so contentious. The author very much agrees with Chiappe in arguing that at present, Protoavis is irrelevant to the phylogenetic reconstruction of Aves. While further material from the Dockum beds may vindicate this peculiar archosaur, for the time being, the case for Protoavis is non-existent." Paleoenvironment The inferred paleoclimate of the Dockum Group would have been subtropical and governed by a distinct dry/wet season pattern, with the latter marked by monsoonal rains. The botanical evidence indicates that the area was densely forested, and the abundance of both invertebrate and vertebrate material from the site suggests that the locale was in general richly populated by a wide variety of species.Ash, S. R. 1972. Upper Triassic Dockum flora of eastern New Mexico and Texas. In New Mexico Geological Society Guide Book, 124-128. Dinosaurs were still fairly rare in the Dockum group, and only some ceratosaurs and other basal forms are well documented.Chatterjee, S. (1984). A new ornithischian dinosaur from the Triassic of North America. Naturewissenschaften 71: 630-631.Chatterjee, S. (1993). Shuvosaurus, a new theropod. National Geographic Research and Exploration 9': 476-491. The principal carnivores of the locale would have been poposaurids such as ''Postosuchus, a species well represented in the Triassic redbeds of Texas. Other archaic archosaurs, such as rhynchosaurs and aetosaurs, were also fairly common. See also *Origin of birds *Origin of avian flight *Feathered dinosaurs *Birds Came First References * John R. Hutchinson (2001). The evolution of femoral osteology and soft tissues on the line to extant birds (Neornithes). Zoological Journal of the Linnean Society '''131:2 169–197. * Currie, P. (1995): New information on the anatomy and relationships of Dromaeosaurus albertensis. Journal of Vertebrate Paleontology 15: 576-591. * Dingus, L. & Rowe, T. (1998): The Mistaken Extinction: Dinosaur Evolution and the Origin of Birds. W. H. Freeman & Company, New York. * Feduccia, A. (1996): The Origin and Evolution of Birds (1st ed.). Yale University Press, New Haven. * Kurochkin, E.N. (1995): Synopsis of Mesozoic birds and early evolution of Class Aves. Archaeopteryx 13: 47-66. * Melchor, Ricardo N.; de Valais, Silvina & Genise, Jorge F. (2002): Bird-like fossil footprints from the Late Triassic. Nature 417: 936-938. (HTML abstract) * Paul, G.S. (1988): Predatory Dinosaurs of the World. Simon & Schuster, New York. * Witmer, L. (1991): Perspectives on avian origins. In: Schultze, H.-P. & Trueb, L. (eds.): Origins of the Higher Groups of Tetrapods: 427-466. * Witmer, L. (1997): Introduction. In: Chatterjee, S.: The Rise of Birds: 225 Million Years of Evolution''. * Witmer, L. (2001): The role of Protoavis in the debate on avian origins. In: Gauthier, J. & Gall, L.F. (eds): New perspectives on the origin and early evolution of birds: 537-548. Special Publication of the Peabody Museum of Natural History, Yale University, New Haven, Conn., USA. ISBN 0-912532-57-2 Category:Dinosaurs of North America Category:Saurischians Category:Triassic dinosaurs Category:Triassic reptiles